Multilayer nonwoven composite structure

ABSTRACT

A nonwoven composite structure is provided which has at least two melt-extruded nonwoven layers: 
     (A) a first layer which includes at least a portion of a first nonwoven web; and 
     (B) a second layer which includes at least a portion of a second nonwovfen web; 
     in which, 
     (1) the boundary between any two adjacent melt-extruded nonwoven layers is indistinct in that fibers at or near the surfaces of such adjacent layers are significantly intermingled; 
     (2) the fibers of at least one of such first and second layers are prepared by melt extrusion through a die at a shear rate of from about 50 to about 30,000 sec -1  and a throughput of no more than about 5.4 kg/cm/hour of a mixture of an additive and a thermoplastic polymer, which additive imparts to the surfaces of the fibers, as a consequence of the preferential migration of the additive to the surfaces of the fibers as they are formed, at least one characteristic which is different from the surface characteristics of fibers prepared from the thermoplastic polymer alone, said preferential migration taking place spontaneously upon the formation of the fibers without the need for a post-formation treatment of any kind; 
     (3) the additive present in any melt-extruded nonwoven layer does not migrate to an adjacent layer to a significant degree in use, so that the surface characteristics of each layer remain substantially as originally prepared; and 
     (4) the composite has been pattern bonded by the application of heat and pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

A multilayer laminated nonwoven structure in which the layers havesurface characteristics similar to those of the layers of the compositestructure of the present invention is described and claimed in copendingand commonly assigned application Ser. No. 618,354, entitled MULTILAYERNONWOVEN LAMINIFEROUS STRUCTURE, filed of even date in the names ofDavid C. Potts, George A. Young, Dennis S. Everhart, J. Gavin MacDonald,and Ronald S. Nohr.

BACKGROUND OF THE INVENTION

The present invention relates to a nonwoven composite structure havingat least two melt-extruded nonwoven layers. More particularly, thepresent invention relates to a nonwoven composite structure having atleast two melt-extruded layers in which the fibers of at least one layerare prepared by melt extrusion of a mixture of an additive and athermoplastic polymer, which additive imparts to the surfaces of saidfibers, as a consequence of the preferential migration of said additiveto the surfaces of said fibers as they are formed, at least onecharacteristic which is different from the surface characteristics offibers prepared from said thermoplastic polymer alone.

Multilayer nonwoven composites and laminates are not new, although theearlier structures differ significantly from those provided by thepresent invention. By way of illustration, some of the earlierstructures are described in the paragraphs which follow.

U.S. Pat. No. 3,770,562 to Newman discloses a composite nonwoven fabric.A soft and flexible spunbonded web is impregnated with a softthermoplastic binder, dried, then plied by heat and pressure to at leastone substantially binder-free fibrous layer. Such fibrous layertypically is a sheet of cellulose tissue, rayon, or cotton card orgarnett web, or the like.

U.S. Pat. Nos. 3,973,068 and 4,070,218 to Weber describe a soft,nonwoven web which is produced by adding directly to a thermoplasticpolymer at the time of extrusion a lubricating agent having and HLBnumber in the range of 8 to 20 and a molecular weight in the range offrom 200 to 4,000. The lubricating agent is uniformly distributed intothe polymer as extruded into filaments. The lubricating agent is forcedto the surfaces of the fibers by subjecting the formed web to astringent heat treatment.

European Patent Application No. 87307470.2, Publication No. 0 260 011A2, describes fluorochemical oxazolidinones. The compounds are stated tobe particularly useful as additives in synthetic organic polymer meltswhich, when melt-extruded, give fibers and films having low surfaceenergies, oil and water repellency, and resistance to soiling. Suitablepolymers include polyamides, polyesters, and polyolefins. ZONYL®fluorochemicals recently were advertised in the Jul. 16, 1990 issue ofChemical and Engineering News as additives for polymers which migrate tothe surface and orient themselves with their perfluoroalkyl groupsfacing outward. Other references relating to the incorporation offluorochemicals into such polymers as polyolefins include, among others,D. R. Thompson et al., "New Fluorochemicals for Protective Clothing,"INDA-TEC 90 Conference, Jun. 5-8, 1990 and U.S. Pat. Nos. 4,855,360 toDuchesne et al. and 4,863,983 to Johnson et al.

Low-temperature-spinnable polypropylene compositions for the preparationof spunbonded nonwovens are described in published Japanese PatentApplication No. 61,155,437 [Chem. Abstr., 105:192786s (1986). Thecompositions contain a crystal-nucleating agent, e.g., 0.065 percentbis(1-tert-butylperoxy-1-methylethyl)benzene and 0.2 percentdibenzylidenesorbitol.

U.S. Pat. No. 3,969,313 to Aishima et al. describes thermoplasticcomposite compositions comprising a thermoplastic material, apolyolefin, and a reactive inorganic filler. The filler is prepared bythe reaction of a metal carbonate, hydroxide, or oxide with a definedunsaturated aliphatic or aromatic carboxylic acid. See also U.S. Pat.No. 3,926,873, also to Aishima et al., which describes a similarcomposition lacking the polyolefin component.

A method of making a structural member from a prepeg sheet of fusibleresin microfibers and heat-resistant reinforcing fibers is described inU.S. Pat. No. 4,104,340 to Ward. Alternating layers of fusible resinmicrofibers and heat-resistant reinforcing fibers such as glass fibersare formed on a moving forming wire. The resulting multi-layered sheetthen is molded under heat and pressure to form the structural member.

U.S. Pat. No. 4,196,245 to Kitson et al. discloses a composite nonwovenfabric comprising adjacent microfine fibers in layers. The fabriccomprises at least two hydrophobic plies of microfine fibers and atleast one nonwoven cover ply which may be an apertured film, aspunbonded ply, or an air-laid, wet-laid, or carded ply of fibers. Thehydrophobic plies typically are prepared by meltblowing.

A disposable absorbent nonwoven structure is described in U.S. Pat. No.4,287,251 to King and Boyd. The structure comprises alternate layers ofabsorbent nonwoven material and nonwoven hydrophobic thermoplasticmaterial, minimally bonded together. The absorbent layers may comprisespunbonded rayon webs or webs or air-laid, wet-laid, or carded rayonfibers of staple length.

U.S. Pat. No. 4,375,718 to Wadsworth and Hersh describes a method ofmaking an electrostatically charged filtration medium. Briefly, a webmade of nonconductive thermoplastic fibers is contacted on each sidewith a more conductive web to form a combined web. The combined web ischarged with electrically charged particles from corona chargingelements on opposite sides of the web. The nonconductive web typicallyis made from polypropylene fibers.

A nonwoven fabric and a method for its production is disclosed in U.S.Pat. No. 4,377,615 to Suzuki and Igaue. The fabric comprises an upperlayer having a substantially smooth surface and a lower layer having adensity lower than that of the upper layer. Both layers are fibrous andcontain adhesive bonding materials.

U.S. Pat. No. 4,436,780 to Hotchkiss et al. describes a nonwoven wiperlaminate. The laminate consists of a relatively high basis weight middlelayer of meltblown thermoplastic microfibers and, on either side, alightweight layer of generally continuous filament thermoplastic fibershaving a larger fiber diameter. A preferred laminate consists of apolypropylene meltblown layer having on either side a polypropylenespunbonded layer. A similar material is described in U.S. Pat. No.4,906,513 to Kebbell and Watts, in which the center meltblown layer hasmixed therein other fibers or particles. See also U.S. Pat. No.4,374,888 to Bornslaeger which describes a similar laminate for arecreation fabric, in which the outer layers are treated for resistanceto ultraviolet radiation and/or flame retardancy. A two-layeredmeltblown-spunbonded fabric is disclosed in U.S. Pat. No. 4,041,203 toBrock and Meitner, and a three-layered fabric comprising a carded websandwiched between two spunbonded layers is described in U.S. Pat. No.4,039,711 to Newman.

U.S. Pat. No. 4,508,113 to Malaney describes a microfine fiber laminate.A preferred embodiment comprises a three-ply hydrophobic microfine fiberstructure sandwiched between and fuse-bonded to two layers of conjugatefibers having a low melting sheath and a high melting core. The innerply of the three-ply structure is relatively high melting while the twoouter plies are low melting.

An extensible microfine fiber laminate is disclosed in U.S. Pat. No.4,555,811 to Shimalla. A preferred embodiment comprises an inner crepedhydrophobic microfine fiber structure sandwiched between and bonded totwo reinforcing layers of nonwoven fibers. The inner structure maycomprise two or more plies bonded together, which plies preferably areprepared by meltblowing a thermoplastic polymer. The reinforcing layerspreferably consist of spunbonded webs made up of sheath/core bicomponentfibers.

U.S. Pat. No. 4,604,313 to McFarland and Lang relates to the selectivelayering of superabsorbents in meltblown substrates. A first layer ofmeltblown fibers containing wood fibers is formed on a continuousforaminous belt. A second layer is formed on the first layer, the secondlayer containing both wood fibers and a superabsorbent and beingintegrally connected to the first layer. See also U.S. Pat. Nos.4,655,757 and 4,724,114, both also to McFarland and Lang.

U.S. Pat. No. 4,610,915 to Crenshaw et al. relates to a two-ply nonwovenfabric laminate. The first ply is a synthetic fibrous nonwoven materialand the second ply is a fibrous nonwoven material. The two plies arebonded together by means of a flexible, soft latex binder whichpenetrates each ply to a depth of from about 20% to about 80% of itsthickness. The first ply typically is a spunbonded web made from athermoplastic polymer, the most common of which are rayon, polyester,polypropylene, and nylon. The second ply can be an air-laid or awet-laid cellulosic pulp sheet, with a tissue sheet being preferred. Seealso U.S. Pat. No. 4,588,457 to Crenshaw et al.

A microporous multilayer nonwoven material for medical applications isdescribed in U.S. Pat. No. 4,618,524 to Groitzsch and Fahrbach. Thematerial consists of a layer of microfibers covered on opposite sideswith nonwoven layers, all of the layers being bonded together with apattern of water repellent and, preferably, elastic paste memberssufficiently penetrating through the layers.

A multilayer nonwoven fabric is disclosed in U.S. Pat. No. 4,668,566 toBraun. Such fabric comprises at least two layers of nonwoven webadjacent and bonded to each other. One of the layers is composed ofpolypropylene fibers and another of the layers is composed ofpolyethylene fibers.

U.S. Pat. No. 4,714,647 to Shipp, Jr. and Vogt describes a meltblownmaterial with a depth fiber size gradient. The material is useful as afilter medium and is formed by sequentially depositing layers ofmeltblown thermoplastic fibers, having the same composition butdifferent sizes, onto a collector. See also U.S. Pat. No. 4,904,521 toJohnson et al. which describes multi-layered nonwoven wiper having anumber of interbonded meltblown layers, in which the inner layers havesmaller average pore sizes for liquid-holding capacity.

U.S. Pat. No. 4,753,843 to Cook and Cunningham describes an absorbent,protective nonwoven fabric. The fabric has one or more center layers ofmeltblown polypropylene microfibers sandwiched between one or moremeltblown surface layers. The surface layers are composed of meltblownpolypropylene microfibers which have been rendered hydrophilic byspraying the fibers as they are formed with an aqueous solution of anonionic surfactant.

A laminated fibrous web is described in U.S. Pat. No. 4,761,322 toRaley. The web comprises a first fibrous layer and a second fibrouslayer, in which the second fibrous layer is bonded to and of lowerdensity than the first fibrous layer. The fibers in the second fibrouslayer are less bonded to one another than fibers in the first fibrouslayer are bonded to one another. In addition, the first and secondfibrous layers are less bonded to each other than fibers in the firstfibrous layer are bonded to one another. Preferably, the fibrous layersare spunbonded nonwoven webs prepared from thermoplastic polymers, suchas polypropylene, polyethylene, polyesters, polyamides, andpolyurethanes. The bonding differences result from and are controlled bythermal pattern-bonding.

U.S. Pat. No. 4,766,029 to Brock et al. discloses a semi-permeablenonwoven laminate useful as a house wrap. The laminate consists of threelayers. The two exterior layers are spunbonded polypropylene and theinterior layer is a two-component meltblown layer of polyethylene andpolypropylene. The laminate is calendared after formation.

A fabric for protective garments is described in U.S. Pat. No. 4,772,510to McClure. The fabric comprises an outer polymeric film of poly(vinylfluoride), poly(vinylidene fluoride), or copolymers thereof, bonded to asecond film of poly(vinyl alcohol) polymer or copolymer which in turn isbonded to a textile fabric which preferably is a nonwoven fabric.Bonding of the various layers is accomplished by known techniques.

A multilayer nonwoven fabric is disclosed in U.S. Pat. No. 4,778,460 toBraun et al. The fabric comprises at least two layers of a nonwoven web,the fibers of at least one web having a bilobal cross-section. In apreferred embodiment, the fabric consists of two layers, with the fibersof the first web having a bilobal cross-section and the fibers of thesecond web having a trilobal or branched cross-section. In anotherpreferred embodiment, the second layer is rendered wettable by eitherincorporating a wetting agent in the polymer before melt-extruding orapplying a solution of a wetting agent to the nonwoven web after it isformed. The fibers can be prepared from a variety of polymers, withpolyolefins being preferred. Suitable melt-extrusion processes includespunbonding and meltblowing, with spunbonding being preferred. Thelayers typically are stabilized by thermal bonding in discrete,compacted areas.

U.S. Pat. No. 4,784,892 to Storey and Maddern discloses a laminatednonwoven material which comprises a layer of a coformed nonwovenmaterial, i.e., meltblown polymeric microfibers intermixed with woodpulp fibers, cellulose fibers, or absorbent or superabsorbent particles,and a layer of meltblown polymeric microfibers which also may be acoformed nonwoven material as already described. Preferably, thelaminate comprises a coformed material sandwiched between to meltblownlayers. The layers are bonded together, such as by ultrasonic energy orheated calendaring rolls. Suitable polymers include polyethylene,polypropylene, polyester, and nylon, although polypropylene ispreferred.

U.S. Pat. No. 4,818,585 to Shipp, Jr. describes an agriculturalprotective fabric which comprises at least two layers. The first layeris a spunbonded nonwoven web prepared from a polymer which is resistantto being degraded by the environment during the growing season. Thesecond layer is a meltblown nonwoven web prepared from a polymer whichdegrades during the growing season. The first layer typically isprepared from polypropylene treated with ultraviolet light stabilizers;"treatment" apparently means incorporation into the polymer beforemelt-processing of an ultraviolet light stabilizing additive. The secondlayer is prepared from polypropylene which has not been so treated.Other polymers can be used for either or both layers and includepolyethylene, polyester, nylon, and the like.

A health-care laminate is described in U.S. Pat. No. 4,818,597 toDaPonte et al. The laminate comprises five layers including a centralmeltblown nonwoven layer made from a polar polymer such aspoly(ethylene-vinyl acetate). Insulative layers are disposed on bothsides of the central layer. The insulative layers are nonwoven meltblownwebs which are formed of the same or different nonpolar, heat-resistantthermoplastic polymers, such as polypropylene and polyethylene. Finally,outer layers on either side of the insulative layers are formed ofnonwoven spunbonded webs. The outer layers may be prepared from the sameor different thermoplastic polymer. Suitable polymers includepolypropylene, polyethylene, ethylene-propylene copolymers, andpolyethylene-polypropylene blends. The layers are calendared andembossed.

International Application No. PCT/GB87/00211, having Publication No. WO87/05952, filed in the names of Maddern and Currie, describes amultilayer nonwoven fabric comprising at least one spunbonded layerwhich has been impregnated with a thermal stabilizing agent before hotcalendaring one at least one side. The thermal stabilizing agentpreferably is a fluorocarbon. The stabilizing agent is stated to form anantistatic and fluid-repellant coating and to resist surface fuzzing ofthe fabric.

Finally, U.S. Pat. No. 3,738,884 to Soehngen describes a nonwoven mat orfabric composed of partially overlapping regions aligned in the machinedirection. While not a true multilayered structure as the term is usedherein, it is noted at this point for the sake of completeness. The mator fabric is produced by having several nozzles aligned generally in thecross direction. The spray patterns may overlap to the extent ofintermingling filaments during the formation of the mat or fabric.Different materials may be sprayed simultaneously from the nozzles togive a fabric characterized by the presence of longitudinally extendingportions or stripes having different visual or structural properties.

Notwithstanding the wide variety of multilayered structures alreadyknown, there still is a need for a multilayered structure composed ofmultiple nonwoven layers, in which the surface characteristics of thefibers making up the layers are determined at will at the time of theformation of the layers, without the need for any external orpostformation treatment of any kind.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a nonwoven compositestructure having at least two melt-extruded nonwoven layers whichcomprises:

(A) a first layer which comprises at least a portion of a first nonwovenweb; and

(B) a second layer adjacent to said first layer which comprises at leasta portion of a second nonwoven web; in which,

(1) the boundary between any two adjacent melt-extruded nonwoven layersis indistinct in that fibers at or near the surfaces of such adjacentlayers are significantly intermingled;

(2) the fibers of at least one of said first and second layers areprepared by melt extrusion through a die at a shear rate of from about50 to about 30,000 sec⁻¹ and a throughput of no more than about 5.4kg/cm/hour of a mixture of an additive and a thermoplastic polymer,which additive (a) is present at a level of from about 0.05 to about 15percent by weight, based on the amount of thermoplastic polymer, and (b)imparts to the surfaces of said fibers, as a consequence of thepreferential migration of said additive to the surfaces of said fibersas they are formed, at least one characteristic which is different fromthe surface characteristics of fibers prepared from said thermoplasticpolymer alone, said preferential migration taking place spontaneouslyupon the formation of said fibers without the need for a post-formationtreatment of any kind;

(3) the additive present in any melt-extruded nonwoven layer does notmigrate to an adjacent layer to s significant degree in use, so that thesurface characteristics of each layer remain substantially as originallyprepared; and

(4) said composite has been pattern bonded by the application of heatand pressure.

The present invention also provides a method of preparing a nonwovencomposite structure having at least two melt-extruded nonwoven layersadjacent to each other in which each melt-extruded nonwoven layercomprises at least a portion of a nonwoven web and the boundary betweenany two adjacent melt-extruded nonwoven layers is indistinct in thatfibers at or near the surfaces of such adjacent layers are significantlyintermingled, which method comprises the steps of:

(A) sequentially melt extruding one or more additional nonwoven websdirectly onto a first melt-extruded nonwoven web; and

(B) pattern bonding the resulting nonwoven composite by the applicationof heat and pressure; in which

(1) the fibers of at least one melt-extruded nonwoven layer are preparedby melt extrusion through a die at a shear rate of from about 50 toabout 30,000 sec⁻¹ and a throughput of no more than about 5.4 kg/cm/hourof a mixture of an additive and a thermoplastic polymer, which additive(a) is present at a level of from about 0.05 to about 15 percent byweight, based on the amount of thermoplastic polymer, and (b) imparts tothe surfaces of said fibers, as a consequence of the preferentialmigration of said additive to the surfaces of said fibers as they areformed, at least one characteristic which is different from the surfacecharacteristics of fibers prepared from said thermoplastic polymeralone, said preferential migration taking place spontaneously upon theformation of said fibers without the need for a post-formation treatmentof any kind; and

(2) the additive present in any melt-extruded nonwoven layer does notmigrate to an adjacent layer to a significant degree in use, so that thesurface characteristics of each layer remain substantially as originallyprepared.

In general, the thermoplastic polymer is selected from the groupconsisting of polyolefins, polyesters, polyetheresters, and polyamides.In preferred embodiments, the thermoplastic polymer is a polyolefin or apolyester. Polyolefins are more preferred, with the preferredpolyolefins being polyethylene and polypropylene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is diagrammatic representation of a cross-sectional view of thecomposite structure of the present invention, enlarged to showindividual fibers to illustrate the indistinct nature of the boundarybetween the first and second layers.

FIGS. 2 and 3 are diagrammatic representations of cross-sectional viewsof preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term "nonwoven composite structure" is meant todefine a structure composed predominantly of melt-extruded nonwovenlayers, at least two of which must be present and adjacent to eachother. Layers other than melt-extruded nonwoven layers can be present,provided such layers are present for purposes not related to the surfacecharacteristics of the melt-extruded nonwoven layers. For example, oneor more air-laid or wet-laid tissue or other cellulosic fiber layers maybe present to provide increased water absorbency. Alternatively, one ormore layers of scrim or similar material may be present to add increasedstrength to the nonwoven composite structure.

The term "melt-extruded" as applied to a nonwoven layer is meant toinclude a nonwoven layer or web prepared by any melt-extrusion processfor forming a nonwoven web in which melt-extrusion to form fibers isfollowed concurrently by web formation on a foraminous support. The termincludes, among others, such well-known processes as meltblowing,coforming, spunbonding, and the like. By way of illustration only, suchprocesses are exemplified by the following references:

(a) meltblowing references include, by way of example, U.S. Pat. Nos.3,016,599 to R. W. Perry, Jr., 3,704,198 to J. S. Prentice, 3,755,527 toJ. P. Keller et al., 3,849,241 to R. R. Butin et al., 3,978,185 to R. R.Butin et al., and 4,663,220 to T. J. Wisneski et al. See, also, V. A.Wente, "Superfine Thermoplastic Fibers", Industrial and EngineeringChemistry, Vol. 48, No. 8, pp. 1342-1346 (1956); V. A. Wente et al.,"Manufacture of Superfine Organic Fibers", Navy Research Laboratory,Washington, D.C., NRL Report 4364 (111437), dated May 25, 1954, UnitedStates Department of Commerce, Office of Technical Services; and RobertR. Butin and Dwight T. Lohkamp, "Melt Blowing - A One-Step Web Processfor New Nonwoven Products", Journal of the Technical Association of thePulp and Paper Industry, Vol. 56, No.4, pp. 74-77 (1973);

(b) coforming references (i.e., references disclosing a meltblowingprocess in which fibers or particles are comingled with the meltblownfibers as they are formed) include U.S. Pat. Nos. 4,100,324 to R. A.Anderson et al. and 4,118,531 to E. R. Hauser; and

(c) spunbonding references include, among others, U.S. Pat. Nos.3,341,394 to Kinney, 3,655,862 to Dorschner et al., 3,692,618 toDorschner et al., 3,705,068 to Dobo et al., 3,802,817 to Matsuki et al.,3,853,651 to Porte, 4,064,605 to Akiyama et al., 4,091,140 to Harmon,4,100,319 to Schwartz, 4,340,563 to Appel and Morman, 4,405,297 to Appeland Morman, 4,434,204 to Hartman et al., 4,627,811 to Greiser andWagner, and 4,644,045 to Fowells.

As already stated, the nonwoven composite structure of the presentinvention has at least two melt-extruded nonwoven layers, i.e., a firstlayer which comprises at least a portion of a first nonwoven web and asecond layer adjacent to said first layer which comprises at least aportion of a second nonwoven web. Because such first and second layersneed not be coterminous with each other or with any other layer whichmay be present, each layer is defined as comprising at least a portionof a nonwoven web.

In general, the required two nonwoven layers are formed by meltextrusion of a thermoplastic polymer. As used herein, the term"thermoplastic polymer" is meant to include a single polymer; blends ormixtures of two or more polymers of the same type or of different types;copolymers, including random, block, or graft copolymers; and the like.Examples of suitable thermoplastic polymers include, by way ofillustration only, polyolefins, such as polyethylene, polypropylene,poly(1-butene), poly(2-butene), poly(1-pentene),poly(2-pentene),poly(3-methyl-1-pentene),poly(4-methyl-1-pentene),1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene,polyisoprene,polychloroprene, polyacrylonitrile, poly(vinyl acetate), poly(vinylidenechloride), polystyrene, and the like; polyesters, such as poly(ethyleneterephthalate), poly(tetramethylene terephthalate),poly(cyclohexylene-1,4-dimethylene terephthalate) orpoly(oxymethylene-1,4-cyclohexylenemethyleneoxyterephthaloyl), and thelike; polyether-esters, such as poly(oxyethylene)-poly(butyleneterephthalate), poly(oxytrimethylene)-poly(butyleneterephthalate),poly(oxytetramethylene)-poly(butylene terephthalate),poly(oxytetramethylene)-poly(ethylene terephthalate), and the like; andpolyamides, such as poly(6-aminocaproic acid) or poly(ε-caprolactam),poly(hexamethylene adipamide), poly(hexamethylene sebacamide),poly(11-aminoundecanoic acid), and the like; and copolymers of theforegoing, such as acrylonitrile-butadiene-styrene (ABS) copolymers, andthe like.

The thermoplastic polymer preferably is selected from the groupconsisting of polyolefins and polyesters. Polyolefins are morepreferred. Even more preferred are those polyolefins which contain onlyhydrogen and carbon atoms and which are prepared by the additionpolymerization of one or more unsaturated monomers. Examples of suchpolyolefins include, among others, polyethylene, polypropylene,poly(1-butene), poly(2-butene), poly(1-pentene), poly(2-pentene),poly(3-methyl-1-pentene), poly(4-methyl-1-pentene),1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene, polyisoprene,polystyrene, and the like. The most preferred polyolefins arepolypropylene and polyethylene.

Said first layer and said second layer must be adjacent to each other.As used herein, the term "adjacent" means that one surface of said firstlayer is substantially contiguous with a surface of said second layer.Thus, a third web which is not a melt-extruded nonwoven web cannot beinterposed between said first layer and said second layer. However, alayer of scrim or similar material can be present therebetween, sincethe large open areas inherent in a scrim material permit said first andsecond layers to be substantially contiguous with each other.

In addition, the boundary between any two adjacent melt-extrudednonwoven layers, including the boundary between said first and secondlayers, must be indistinct in that fibers at or near the surfaces ofsuch layers are significantly intermingled. Such intermingling is simplythe natural result of forming one melt-extruded nonwoven web directly ontop of another melt-extruded nonwoven web. This requisite interminglingis illustrated in diagrammatic form by FIG. 1 which shows an enlargedboundary-area portion of a nonwoven composite structure of the presentinvention, which composite structure consists only of said first andsecond melt-extruded nonwoven webs. In FIG. 1, nonwoven compositestructure 10 consists of melt-extruded nonwoven layer 11 andmelt-extruded nonwoven layer 12. Melt-extruded nonwoven layer 11 is madeup of fibers 13 and melt-extruded layer 12 is made up of fibers 14.Because of the random manner in which fibers 13 are laid down to formlayer 11, internal voids 15 and surface voids 16 result. As layer 12 isformed on top of layer 11, fibers 14 are laid down randomly, with someof fibers 14 entering or partially filling surface voids 16 of layer 11.Consequently, the boundary between layer 11 and layer 12 is indistinctin that fibers 13 of layer 11 and fibers 14 of layer 12 at or near thesurfaces of such layers are significantly intermingled.

In addition to the intermingling requirement, the fibers of at least oneof said first and second layers are prepared by melt extrusion through adie at a shear rate of from about 50 to about 30,000 sec⁻¹ and athroughput of no more than about 5.4 kg/cm/hour of a mixture of anadditive and a thermoplastic polymer, which additive (a) is present at alevel of from about 0.05 to about 15 percent by weight, based on theamount of thermoplastic polymer, and (b) imparts to the surfaces of saidfibers, as a consequence of the preferential migration of said additiveto the surfaces of said fibers as they are formed, at least onecharacteristic which is different from the surface characteristics offibers prepared from said thermoplastic polymer alone, said preferentialmigration taking place spontaneously upon the formation of said fiberswithout the need for a post-formation treatment of any kind.

As stated above, fibers are formed by extruding the molten mixturethrough a die. Although the nature of the die is not known to becritical, it most often will have a plurality of orifices arranged inone or more rows extending the full machine width. Such orifices may becircular or noncircular in cross-section. The fibers extruded may beeither continuous or discontinuous.

In general, the shear rate will be in the range of from about 50 toabout 30,000 sec⁻¹. Preferably, the shear rate will be in the range offrom about 150 to about 5,000 sec⁻¹, and most preferably from about 300to about 2,000 sec⁻¹.

Throughput is of importance because it affects the time the newly formedfiber is in a sufficiently molten or fluid state to allow migration orsegregation of the additive toward the newly formed surfaces, eventhough throughput also affects the shear rate.

Throughput typically will be in the range of from about 0.01 to about5.4 kg/cm/hour. Preferably, throughput will be in the range from about0.1 to about 4.0 kg/cm./hour. The throughput most preferably will be inthe range of from about 0.5 to about 2.5 kg/cm/hour.

As used herein, the phrase "molten state" does not necessarily mean"flowable". Rather, the term is used to denote a condition of thethermoplastic composition in which the additive molecules still arecapable of migrating or segregating to the surface of the newly formedfiber. Thus, the term is somewhat imprecise and not readily subject toaccurate measurement. Consequently, this composition fluidity factorpreferentially is described or accounted for by the term "throughput".

The term "additive" is used throughout this specification and the claimsto include a single compound or a mixture of two or more compounds.Moreover, the additive can be monomeric, oligomeric, or polymeric. Whilethe additive can be either a liquid or a solid, a liquid is preferred.It also is preferred that a liquid additive have a surface tension whichis less than that of virgin polymer; the lower surface tension assuresthat the additive will be more likely to completely "wet" or cover thesurface of the fiber or film as the segregation process proceeds tocompletion, especially under conditions favoring a large concentrationdifferential.

The nature of the additive is not known to be critical, provided theadditive (1) migrates to the surfaces of the fibers as they are formedduring the melt-extrusion process and (2) contains at least onefunctional group which imparts to the surfaces of the fibers at leastone characteristic which is different from the surface characteristicsof fibers prepared from the thermoplastic polymer alone. Examples ofdesired surface characteristics include, among others, hydrophilicity orwater-wettability, alcohol repellency, hydrophobicity, antistaticproperties, and the like. As a practical matter, the more desiredsurface characteristics are water-wettability (hydrophilicity),antistatic properties, and alcohol repellency.

Additives which impart wettability to the surfaces of the nonwovenfibers, as a consequence of the preferential migration of the additiveto the surfaces of the fibers as they are formed, typically aresiloxane-containing compounds. Preferably, the additive will have atleast two moieties, A and B, in which:

(A) moiety A and moiety B act as a single molecular unit which iscompatible with the polymer at melt extrusion temperatures but isincompatible at temperatures below melt extrusion temperatures, but eachof moiety A and moiety B, taken as separate molecular units, isincompatible with the polymer at melt extrusion temperatures and attemperatures below melt extrusion temperatures; and

(B) moiety B has at least one functional group which impartswater-wettability to the nonwoven fibers as they are formed by amelt-extrusion process.

More preferably, the siloxane-containing additive will have the generalformula, ##STR1## in which: (A) R₁ -R₉ are independently selectedmonovalent C₁ -C₃ alkyl groups;

(B) R₁₀ is hydrogen or a monovalent C₁ -C₃ alkyl group;

(C) m represents an integer of from 1 to about 4;

(D) n represents an integer of from 0 to about 3;

(E) the sum of m and n is in the range of from 1 to about 4;

(F) p represents an integer of from 0 to about 5;

(G) x represents an integer of from 1 to about 10;

(H) y represents an integer of from 0 to about 5;

(I) the ratio of x to y is equal to or greater than 2; and

(J) said additive has a molecular weight of from about 350 to about1,400.

In preferred embodiments, each of R₁ -R₁₀ is a methyl group. In otherpreferred embodiments, R₁₀ is either hydrogen or a methyl group. In yetother preferred embodiments, m is either 1 or 2. In still otherpreferred embodiments, p is either 1 or 2, but most preferably is 2. Inyet other preferred embodiments, y is 0 and x is 7 or 8.

Preferably, n will be 0, in which case the additive will have thegeneral formula, ##STR2## in which each of R₁ -R₁₀, m, p, x, and y areas already defined.

While the additive molecular weight can vary from about 350 to about1,400, it preferably will not exceed about 1,000. Most preferably, themolecular weight will be in the range of from about 350 to about 700.

Examples of especially useful additives coming within general formula Iare the following:

Additive A

Additive A is a trisiloxane polyether, PS-071, supplied by PetrarchSystems, Bristol, Pa. The material has the formula, ##STR3## Thematerial has a theoretical molecular weight of 646. Based on gelpermeation chromatography studies (American Polymer StandardsCorporation, Mentor, Ohio) relative to PDMS standards, the followingaverage molecular weights were calculated:

Weight-average molecular weight: 581

Number-average molecular weight: 544

Z-average molecular weight: 610

Polydispersity: 1.07

The material contained an estimated 3.6 percent low molecular weightmaterial, based on total peak area and main peak area comparisons, andan estimated 10-16 percent free polyether.

Additive B

This additive also is a trisiloxane polyether, L-77, supplied by UnionCarbide Corporation, Danbury, Conn., which differs from Additive Aprimarily in having one less oxyethylene group (i.e., n is 7, ratherthan 8).

The material has a theoretical molecular weight of 602. Based on gelpermeation chromatography studies (American Polymer StandardsCorporation, Mentor, Ohio) relative to PDMS standards, the followingaverage molecular weights were calculated:

Weight-average molecular weight: 557

Number-average molecular weight: 480

Z-average molecular weight: 614

Polydispersity: 1.16

The material contained an estimated 7.8 percent low molecular weightmaterial, based on total peak area and main peak area comparisons, andan estimated 20-25 percent free polyether.

Additive C

Additive C is a polysiloxane polyether, T-5878, supplied by Th.Goldschmidt AG, Essen, Federal Republic of Germany. The material isessentially the same as Additive A.

Based on gel permeation chromatography studies (American PolymerStandards Corporation, Mentor, Ohio) relative to PDMS standards, thefollowing average molecular weights were calculated:

Weight-average molecular weight: 602

Number-average molecular weight: 527

Z-average molecular weight: 672

Polydispersity: 1.14

The material contained an estimated 9.8 percent low molecular weightmaterial, based on total peak area and main peak area comparisons, andan estimated 20-25 percent free polyether.

Additive D

This additive is another trisiloxane polyether, T-5847, which differsfrom Additive A primarily in having two additional oxyethylene groups(i.e., n is 10, rather than 8), and two oxypropylene groups (not shownin the formula for Additive A). In addition, the terminal group of thepoly(oxyalkylene) moiety is hydrogen rather than a methyl group.

The material has a theoretical molecular weight of 790, a weight-averagemolecular weight of 836, and a polydispersity of 1.20. It is supplied byTh. Goldschmidt AG.

Additive E

The additive is a trisiloxane polyether, G-1255, supplied by Th.Goldschmidt AG, Essen. The material is similar to Additive A, exceptthat the polyether moiety consists of six ethyleneoxy units and is notend-capped, the weight-average molecular weight is 610, and thepolydispersity is 1.09. The material contained about 11 percent byweight of free polyether.

Additive F

Additive F is a polysiloxane polyether having the formula, ##STR4## Thematerial is available from Th. Goldschmidt Ag, Essen, Federal Republicof Germany, as T-3004. It has a molecular weight of 852 and a viscosityat 25° of 23 centistokes. A 1 percent by weight aqueous solution of theadditive has a cloud point of less than 3° and a surface tension of25.2±1.5 dynes/cm.

While antistatic properties can be provided by a number of additives, ithas been found that some additives which provide water-wettability alsocan impart antistatic properties. For example, Additive E can render anonwoven web water-wettable at additive levels as low as 0.3 percent byweight, based on the amount of thermoplastic polymer. At a level ofabout 1.5 percent by weight, however, the resulting nonwoven web notonly is water-wettable, but it also exhibits antistatic properties.

Alcohol-repellant additives typically are fluorine-containing materials.Examples of especially suitable fluorine-containing additives are thefollowing:

Additive G

This additive is a perfluoroalkyl urethane, L-8977, which is availablefrom 3M Company, St. Paul, Minn. The material is a white powder having amelting point of 130°-138° C. No other information regarding thematerial is available.

Additive H

This additive is similar to Additive G and is available from the samesource as L-8982. No information regarding the material is available.

Additive I

Additive I is any one of the Krytox™ polymers obtained by thecondensation polymerization of perfluoropropylene oxide. The materialsare available from E. I. duPont de Nemours & Company, Wilmington, Del.

Additive J

The additive, MPD-7901, available from duPont, is a2-perfluoroalkylethyl acetate. It has a melting point of 23°-24° C. andnegligible solubility in water.

Additive K

This additive is a 2-perfluoroalkylethyl hexanoate, available fromduPont as MPD-7902. It has a melting point of 30°-50° C. and negligiblesolubility in water.

Additive L

Additive L is MPD-7903, available from duPont. The material is anaddition copolymer consisting of 85 mole-percent 2-perfluoroalkylethylmethacrylate and 15 mole-percent 2-diethylaminoethyl methacrylate. Thematerial has negligible solubility in water.

Additive M

This additive, MPD-7708, is an addition copolymer of2-perfluoroalkylethyl methacrylate and 2-ethylhexyl methacrylate. Thematerial is available from duPont. It is a weakly acidic tacky solidhaving a melting point of 62°-72° C. The material is dispersible inwater.

Additive N

The additive, MPD-7709, is available from duPont and is aperfluoroalkyl-substituted urethane mixture. The material is acrystalline solid which is dispersible in water. It has a melting pointof 88°-95° C.

Additive O

This additive is Telomer™ B Citrate or Zonyl® TBC, available fromduPont. The material is a 2-perfluoroalkyl-ethyl citrate. It is waxysolid having a melting point of 50°-80° C. and negligible solubility inwater. It has a specific gravity of 1.5 at 25° C.

Additive P

Additive P is Telomer™ B Citrate Urethane, available from duPont.

Additive Q

The additive, available from duPont, is Zonyl™ FTS, a2-perfluoroalkylethyl stearate. The material has a melting point of30°-45° C., with negligible solubility in water.

Additive R

This additive is Zonyl™ TBS, available from duPont. The material is amixture of a 2-perfluoroalkylethylsulfonic acid and its ammonium salt.

Additive S

Additive S is Zonyl™ UR. The material, available from duPont, is a2-perfluoroalkylethylphosphate having an unknown cation.

In general, additive will be present in a melt-extruded nonwoven web inan amount of from about 0.05 to about 15 percent by weight, based on theamount of thermoplastic polymer from which the web is formed. As apractical matter, additive levels of from about 0.1 to about 5 percentby weight are preferred, with additive levels of from about 0.1 to about2 percent by weight being most preferred.

As already noted, the additive preferentially migrates to the surfacesof the melt-extruded fibers as they are formed. Thus, the additiveimparts to the surfaces of the fibers at least one characteristic whichis different from the surface characteristics of fibers prepared in theabsence of the additive. However, the additive present in anymelt-extruded nonwoven layer must not migrate to an adjacent layer to asignificant degree in use, so that the surface characteristics of eachlayer remain substantially as originally prepared. That is, once havingmigrated to the surfaces of the fibers, significant further migration toan adjacent layer does not occur.

Finally, the nonwoven composite structure is pattern bonded by theapplication of heat and pressure. Preferably, such application of heatand pressure will be in the ranges of from about 80° C. to about 180° C.and from about 150 to about 1,000 pounds per linear inch (59-178 kg/cm),respectively. More preferably, a pattern having from about 10 to about250 bonds/inch² (1-40 bonds/cm²) covering from about 5 to about 30percent of the wipe surface area will be employed.

Such pattern bonding is accomplished in accordance with knownprocedures. See, for example, U.S. Des. Pat. No. 239,566 to Vogt, U.S.Des. Pat. No. 264,512 to Rogers, U.S. Pat. No. 3,855,046 to Hansen etal., and U.S. Pat. No. 4,493,868 to Meitner for illustrations of bondingpatterns and a discussion of bonding procedures.

In view of the foregoing description, it should be apparent thatnumerous combinations and permutations of the present invention arepossible, two of which are illustrated by FIGS. 2 and 3.

The most basic embodiment of the present invention is illustrated byFIG. 2 which is a cross-sectional representation of a compositestructure of the present invention having two layers. In FIG. 2,composite structure 20 consists of melt-extruded nonwoven layers 21 and22 having indistinct boundary 23. Examples of combinations of layers 21and 22 which come within the scope of the present invention include,among others, the following:

Combination 2-1

Layer 21: A polypropylene meltblown web.

Layer 22: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Combination 2-2

Layer 21: A polyethylene meltblown web.

Layer 22: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Combination 2-3

Layer 21: A polypropylene spunbonded web.

Layer 22: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Combination 2-4

Layer 21: A polypropylene meltblown web.

Layer 22: A polypropylene spunbonded web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Combination 2-5

Layer 21: A polypropylene spunbonded web.

Layer 22: A polypropylene spunbonded web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Combination 2-6

Layer 21: A polypropylene meltblown web.

Layer 22: A polypropylene meltblown web containing an additive whichrenders the fibers alcohol repellant.

Combination 2-7

Layer 21: A coformed web in which wood pulp has been comingled withmeltblown polypropylene fibers.

Layer 22: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Combination 2-8

Layer 21: A polypropylene meltblown web.

Layer 22: A coformed web in which wood pulp has been comingled withpolypropylene meltblown fibers containing an additive which renders thefibers hydrophilic (water-wettable).

Combination 2-9

Layer 21: A polypropylene meltblown web containing an additive whichrenders the fibers alcohol repellant.

Layer 22: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Combination 2-10

Layer 21: A polypropylene spunbonded web containing an additive whichrenders the fibers alcohol repellant.

Layer 22: A polypropylene spunbonded web containing an additive whichrenders the fibers hydrophilic (water-wettable).

If desired to give added strength to the composite structure, a layer ofscrim can be placed between layers 21 and 22. As used herein, the term"scrim" is meant to include any open-mesh material, whether woven ornonwoven, which generally is used as a reinforcing material. For anexample of a nonwoven scrim material, see, by way of illustration only,U.S. Pat. No. 3,652,374 to Condon.

A cross-sectional representation of a three-layer nonwoven compositestructure is shown in FIG. 3. In FIG. 3, composite structure 30 consistsof melt-extruded nonwoven layers 31 and 32 having indistinct boundary33. Third layer 34 is located adjacent to layer 32, and layers 32 and 34have boundary 35 which may be either indistinct or distinct. If eitherof layers 32 and 34 is melt-extruded directly onto the other, boundary35 will be indistinct. However, if layers 32 and 34 are brought togetherafter being formed, then boundary 35 will be distinct; that is, thefibers at or near the surfaces of the two layers will not besignificantly intermingled.

Examples of combinations of layers 31, 32, and 34 include, among others,the following (boundary 33 between layers 31 and 32 is indistinct ineach combination):

Combination 3-1

Layer 31: A polypropylene meltblown web.

Layer 32: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Layer 34: A polypropylene meltblown web.

Boundary 35: Indistinct.

Combination 3-2

Layer 31: A polyethylene meltblown web.

Layer 32: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Layer 34: A polypropylene spunbonded web.

Boundary 35: Indistinct.

Combination 3-3

Layer 31: A polypropylene meltblown web.

Layer 32 A polypropylene meltblown web containing an additive whichrenders the fibers alcohol repellant.

Layer 34: A polyethylene meltblown web.

Boundary 35: Indistinct.

Combination 3-4

Layer 31: A polyethylene meltblown web.

Layer 32: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Layer 34: A polyethylene meltblown web.

Boundary 35: Indistinct.

Combination 3-5

Layer 31: A polypropylene meltblown web.

Layer 32: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Layer 34: A polyester bonded carded web.

Boundary 35: Distinct.

Combination 3-6

Layer 31: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water-wettable).

Layer 32: A polypropylene meltblown web containing an additive whichrenders the fibers alcohol repellant.

Layer 34: A coformed web in which wood pulp has been comingled withpolypropylene meltblown fibers.

Boundary 35: Indistinct.

Combination 3-7

Layer 31: A polypropylene spunbonded web.

Layer 32: A polypropylene meltblown web containing an additive whichrenders the fibers hydrophilic (water wettable).

Layer 34: A polypropylene spunbonded web.

Boundary 35: Indistinct.

Combination 3-8

Layer 31: A polypropylene spunbonded web.

Layer 32: A polypropylene meltblown web containing an additive whichrenders the fibers alcohol repellant.

Layer 34: A polypropylene spunbonded web.

Boundary 35: Indistinct.

Combination 3-9

Layer 31: A polypropylene spunbonded web containing an additive whichrenders the fibers alcohol repellant.

Layer 32: A polypropylene meltblown web.

Layer 34: A polypropylene spunbonded web containing an additive whichrenders the fibers alcohol repellant.

Boundary 35: Indistinct.

If desired, a layer of scrim can be placed between layers 31 and 32and/or between layers 32 and 34 in any of the foregoing combinations.

In general, the number of layers in the nonwoven composite structure ofthe present invention is limited only by cost and performanceconsiderations. In some cases, more than three layers will beappropriate. For example, a medical fabric often is constructed of atleast three layers as represented by combinations 3-7, 3-8, and 3-9, byway of illustration only. Such a combination, often referred to as anSMS composite, couples the barrier properties of a meltblown web withthe strength and abrasion resistance of spunbonded webs. The use ofadditional meltblown layers, for example, permits the retention of thebasic features of an SMS composite while at the same time takingadvantage of the differentiation in surface properties permitted by thepresent invention.

By way of illustration, one embodiment of a five-layer medical fabricconsists of three central meltblown layers sandwiched between two outerspunbonded layers. All of the layers except the center-most meltblownlayer contain an additive which renders the fibers alcohol repellant.The center-most meltblown layer contains an additive which renders thefibers antistatic. Alternatively, all but one of the outer spunbondedlayers can contain an additive which renders the fibers alcoholrepellant, with the remaining outer spunbonded layer containing anadditive which renders the fibers antistatic.

In general, the nonwoven composite structure of the present invention ismade by the method which comprises the steps of:

(A) sequentially melt extruding one or more additional nonwoven websdirectly onto a first melt-extruded nonwoven web; and

(B) pattern bonding the resulting nonwoven composite by the applicationof heat and pressure; in which

(1) the fibers of at least one melt-extruded nonwoven layer are preparedby melt extrusion through a die at a shear rate of from about 50 toabout 30,000 sec⁻¹ and a throughput of no more than about 5.4 kg/cm/hourof a mixture of an additive and a thermoplastic polymer, which additiveimparts to the surfaces of said fibers, as a consequence of thepreferential migration of said additive to the surfaces of said fibersas they are formed, at least one characteristic which is different fromthe surface characteristics of fibers prepared from said thermoplasticpolymer alone, said preferential migration taking place spontaneouslyupon the formation of said fibers without the need for a post-formationtreatment of any kind; and

(2) the additive present in any melt-extruded nonwoven layer does notmigrate to an adjacent layer to a significant degree in use, so that thesurface characteristics of each layer remain substantially as originallyprepared.

As indicated earlier, the formation of a melt-extruded nonwoven web iscarried out by methods well known to those having ordinary skill in theart, such as by meltblowing, coforming, and spunbonding.

The sequential melt-extrusion of one or more additional nonwoven websdirectly onto a first melt-extruded nonwoven web also can be carried outin accordance with known procedures. For example, a second nonwoven webcan be melt-extruded directly onto a first, preformed nonwoven web.Alternatively, both a first nonwoven web and a second nonwoven web canbe melt-extruded sequentially on a multiple-bank melt-extrusionapparatus. See, by way of example only, U.S. Pat. Nos. 4,714,647 toShipp, Jr. et al., 4,761,322 to Raley, 4,766,029 to Brock et al.,4,778,460 to Braun et al., 4,784,892 to Maddern et al., 4,818,585 toShipp, Jr., and 4,818,597 to DaPonte et al., each of which isincorporated herein by reference. The pattern bonding of the resultingnonwoven composite then is accomplished as already described.

The present invention is further described by the example which follows.Such example, however, is not to be construed as limiting in any wayeither the spirit or scope of the present invention. In the example, alltemperatures are in degrees Celsius and all parts are by weight unlessstated otherwise.

EXAMPLE Preparation of a Composite Structure Having Combination 2-10

The thermoplastic polymer employed in this example was Type PF-444polypropylene (Himont Incorporated, Wilmington, Del.) having a melt flowrate of 60 as determined by ASTM Test Method D1238-82, "Standard TestMethod for Flow Rates of Thermoplastics by Extrusion Plastometer".According to the manufacturer, the polymer had number average molecularweight of 30,000 and a polydispersity of 4.0.

A Henschel Fluidizing Mixer (Model FM 10 "C", Thyssen Henschel, 3500Kassel 2 Postfach 102969, Federal Republic of Germany) was charged withpolypropylene granules and 1.0 percent by weight, based on the amount ofpolypropylene, of Additive G. The mixer was run until the temperaturereached about 140°.

A spunbonded web was prepared from the resulting coated polypropylenegranules on a small pilot-scale apparatus essentially as described inU.S. Pat. No. 3,341,394 to Kinney as modified by U.S. Pat. No. 3,655,862to Dorschner et al., both of which patents being incorporated herein byreference. The apparatus utilized a barrel having three heating zones.The web was formed on a polyethylene spunbonded web having a basisweight of about 19 grams per square meter (g/m² or gsm) which served asa carrier sheet. The resulting web was compressed and rolled.

The basic process parameters were as follows:

Barrel zone 1 temperature, 212°;

Barrel zone 2 temperature, 228°;

Barrel zone 3 temperature, 230°;

Barrel pressure, 410-480 psi;

Spin pump temperature, 233°; and

Spin pump pressure, 89-98 psi.

The line speed was about 7 feet per minute (about 3.6 cm/sec), whichresulted in a web having a basis weight of about 71 gsm.

A second spunbonded web was produced in a similar manner, except thatadditive G was replaced with 1.5 percent by weight, based on the amountof polypropylene, of additive F.

The basic process parameters for the second spunbonded web were asfollows:

Barrel zone 1 temperature, 212°;

Barrel zone 2 temperature, 226°;

Barrel zone 3 temperature, 231°;

Barrel pressure, 250-300 psi;

Spin pump temperature, 233°; and

Spin pump pressure, 98-110 psi.

As before, the line speed was about 7 feet per minute (about 3.6cm/sec), again resulting in a web having a basis weight of about 71 gsm.The web was formed on the first web by unrolling the first web/carriersheet combination at a rate equal to the line speed of the spunbondingapparatus. The resulting two-layer nonwoven composite structure/carriersheet combination was pattern bonded essentially as described in U.S.Pat. No. 3,885,046 to Hansen et al., supra. The bonding temperature was135° and the calendar roll temperature was 104°. The gauge pressure forthe bonding roll was 15 psi. The bonding line speed was 7 feet perminute (about 3.6 cm/sec). The bond pattern had 107 bonds/inch² (about16.6 bonds/cm²), with the bonded portions constituting about 14 percentof the total surface area.

After bonding, the carrier sheet was readily removed from the two-layernonwoven composite structure. Such structure had one layer which wasalcohol repellant and another layer which was water-wettable orhydrophilic.

Having thus described the invention, numerous changes and modificationsthereof will be apparent to those having ordinary skill in the artwithout departing from the spirit or scope of the invention.

What is claimed is:
 1. A nonwoven composite structure having at leasttwo melt-extruded nonwoven layers which comprises:(A) a first layerwhich comprises at least a portion of a first nonwoven web; and (B) asecond layer adjacent to said first layer which comprises at least aportion of a second nonwoven web;in which, (1) the boundary between anytwo adjacent melt-extruded nonwoven layers is indistinct in that fibersat or near the surfaces of such adjacent layers are significantlyintermingled; (2) the fibers of at least one of said first and secondlayers are prepared by melt extrusion through a die at a shear rate offrom about 50 to about 30,000 sec⁻¹ and a throughput of no more thanabout 5.4 kg/cm/hour of a mixture of an additive and a thermoplasticpolymer, which additive imparts to the surfaces of said fibers, as aconsequence of the preferential migration of said additive to thesurfaces of said fibers as they are formed, at least one characteristicwhich is different from the surface characteristics of fibers preparedfrom said thermoplastic polymer alone, said preferential migrationtaking place spontaneously upon the formation of said fibers without theneed for a post-formation treatment of any kind; (3) the additivepresent in any melt-extruded nonwoven layer does not migrate to anadjacent layer to a significant degree in use, so that the surfacecharacteristics of each layer remain substantially as originallyprepared; (4) said thermoplastic polymer is selected from the groupconsisting of polyolefins, polyesters, polyetheresters, and polyamides;and (5) said composite has been pattern bonded by the application ofheat and pressure.
 2. The nonwoven composite structure of claim 1, inwhich said thermoplastic polymer is a polyolefin or a polyester.
 3. Thenonwoven composite structure of claim 2, in which said thermoplasticpolymer is polyethylene or polypropylene.
 4. The nonwoven compositestructure of claim 3, in which the fibers of said at least one layer arehydrophilic.
 5. The nonwoven composite structure of claim 4, in whichsaid additive is a siloxane-containing additive.
 6. The nonwovencomposite structure of claim 5, in which said siloxane-containingadditive has at least two moieties, A and B, in which:(A) said additiveis compatible with said thermoplastic polymer at melt extrusiontemperatures but is incompatible at temperatures below melt extrusiontemperatures, but each of moiety A and moiety B, if present as separatecompounds, would be incompatible with said thermoplastic polymer at meltextrusion temperatures and at temperatures below melt extrusiontemperatures; (B) moiety B has at least one functional group which is apoly(oxyalkylene) moiety; (C) the molecular weight of said additive isin the range of from about 400 to about 15,000; and (D) said additive ispresent at a level of from about 0.05 to about 15 percent by weight,based on the amount of thermoplastic polymer.
 7. The nonwoven compositestructure of claim 3, in which the fibers of said at least one layer arealcohol repellant.
 8. The nonwoven composite structure of claim 7, inwhich said additive is a fluorocarbon compound.
 9. The nonwovencomposite structure of claim 1, in which said first layer comprisesfibers prepared by melt extrusion of a first thermoplastic polymer andsaid second layer comprises fibers prepared by melt extrusion of asecond thermoplastic polymer.
 10. The nonwoven composite structure ofclaim 9, in which said first thermoplastic polymer and said secondthermoplastic polymer are the same.
 11. The nonwoven composite structureof claim 1, in which said composite has been pattern bonded by theapplication of heat and pressure in the ranges of from about 80° C. toabout 180° C. and from about 150 to about 1,000 pounds per linear inch,respectively, employing a pattern with from about 10 to about 250bonds/inch² (1-40 bonds/cm²) covering from about 5 to about 30 percentof the wipe surface area.
 12. The nonwoven composite structure of claim1, in which said structure consists essentially of a centerpolypropylene meltblown layer sandwiched between two polypropylenespunbonded layers, in which:(A) the boundaries between adjacent layersare indistinct; and (B) said meltblown layer contains an additive whichrenders the fibers alcohol repellant.
 13. The nonwoven compositestructure of claim 12, in which said composite has been pattern bondedby the application of heat and pressure in the ranges of from about 80°C. to about 180° C. and from about 150 to about 1,000 pounds per linearinch, respectively, employing a pattern with from about 10 to about 250bonds/inch² (1-40 bonds/cm²) covering from about 5 to about 30 percentof the wipe surface area.
 14. The nonwoven composite structure of claim1, in which said structure consists essentially of the following fivelayers in the order given:(A) a polypropylene spunbonded layer whichcontains an additive which renders the fibers alcohol repellant; (B) apolypropylene meltblown layer which contains an additive which rendersthe fibers alcohol repellant; (C) a polypropylene meltblown layer whichcontains an additive which renders the fibers antistatic; (D) apolypropylene meltblown layer which contains an additive which rendersthe fibers alcohol repellant; and (E) a polypropylene spunbonded layerwhich contains an additive which renders the fibers alcohol repellant;inwhich the boundaries between adjacent layers are indistinct.
 15. Thenonwoven composite structure of claim 14, in which said composite hasbeen pattern bonded by the application of heat and pressure in theranges of from about 80° C. to about 180° C. and from about 150 to about1,000 pounds per linear inch, respectively, employing a pattern withfrom about 10 to about 250 bonds/inch² (1-40 bonds/cm²) covering fromabout 5 to about 30 percent of the wipe surface area.
 16. The nonwovencomposite structure of claim 1, in which said structure consistsessentially of the following five layers in the order given:(A) apolypropylene spunbonded layer which contains an additive which rendersthe fibers alcohol repellant; (B) a polypropylene meltblown layer whichcontains an additive which renders the fibers alcohol repellant; (C) apolypropylene meltblown layer which contains an additive which rendersthe fibers alcohol repellant; (D) a polypropylene meltblown layer whichcontains an additive which renders the fibers alcohol repellant; and (E)a polypropylene spunbonded layer which contains an additive whichrenders the fibers antistatic;in which the boundaries between adjacentlayers are indistinct.
 17. The nonwoven composite structure of claim 16,in which said composite has been pattern bonded by the application ofheat and pressure in the ranges of from about 80° C. to about 180° C.and from about 150 to about 1,000 pounds per linear inch, respectively,employing a pattern with from about 10 to about 250 bonds/inch² (1-40bonds/cm² ) covering from about 5 to about 30 percent of the wipesurface area.
 18. A method of preparing a nonwoven composite structurehaving at least two melt-extruded nonwoven layers adjacent to each otherin which each melt-extruded nonwoven layer comprises at least a portionof a nonwoven web and the boundary between any two adjacentmelt-extruded nonwoven layers is indistinct in that fibers at or nearthe surfaces of such adjacent layers are significantly intermingled,which method comprises the steps of:(A) sequentially melt extruding oneor more additional nonwoven webs directly onto a first melt-extrudednonwoven web; and (B) pattern bonding the resulting nonwoven compositeby the application of heat and pressure;in which (1) the fibers of atleast one melt-extruded nonwoven layer are prepared by melt extrusionthrough a die at a shear rate of from about 50 to about 30,000 sec⁻¹ anda throughput of no more than about 5.4 kg/cm/hour of a mixture of anadditive and a thermoplastic polymer, which additive imparts to thesurfaces of said fibers, as a consequence of the preferential migrationof said additive to the surfaces of said fibers as they are formed, atleast one characteristic which is different from the surfacecharacteristics of fibers prepared from said thermoplastic polymeralone, said preferential migration taking place spontaneously upon theformation of said fibers without the need for a post-formation treatmentof any kind; (2) said thermoplastic polymer is selected from the groupconsisting of polyolefins, polyesters, polyetheresters, and polyamides;and (3) the additive present in any melt-extruded nonwoven layer doesnot migrate to an adjacent layer to a significant degree in use, so thatthe surface characteristics of each layer remain substantially asoriginally prepared.
 19. The method of claim 18, in which saidthermoplastic polymer is a polyolefin or a polyester.
 20. The method ofclaim 19, in which said thermoplastic polymer is polyethylene orpolypropylene.
 21. The method of claim 18, in which said first layercomprises fibers prepared by melt extrusion of a first thermoplasticpolymer and said second layer comprises fibers prepared by meltextrusion of a second thermoplastic polymer.
 22. The method of claim 21,in which each of said first thermoplastic polymer and said secondthermoplastic polymer is a polyolefin or a polyester.
 23. The method ofclaim 22, in which each of said first thermoplastic polymer and saidsecond thermoplastic polymer is the same polyolefin or polyester. 24.The method of claim 18, in which said nonwoven composite structure hasbeen pattern bonded by the application of heat and pressure in theranges of from about 80° C. to about 180° C. and from about 150 to about1,000 pounds per linear inch, respectively, employing a pattern withfrom about 1 10 to about 250 bonds/inch² (1-40 bonds/cm²) covering fromabout 5 to about 30 percent of the wipe surface area.
 25. An article ofmanufacture which comprises the nonwoven composite structure of claim 1.26. An article of manufacture which comprises the nonwoven compositestructure of claim
 2. 27. An article of manufacture which comprises thenonwoven composite structure of claim
 13. 28. An article of manufacturewhich comprises the nonwoven composite structure of claim
 15. 29. Anarticle of manufacture which comprises the nonwoven composite structureof claim 17.